Cellulose acetate and method for producing cellulose acetate

Abstract

To provide low substituted cellulose acetate having biodegradability and susceptible to metabolically breakdown due to bacteria in intestines and its manufacturing method.SOLUTION: Cellulose acetate having a total degree of acetyl substitution of 0.4 or larger and 0.9 or smaller, a ratio of the acetyl substitution degree at 6-th site in the total degree of acetyl substitution of 0% or larger and 18% or smaller, and light transmittance at 660 nm of 4 wt.% aqueous solution of 5% or larger. A manufacturing method of the cellulose acetate comprises the steps of: deacetylating by subjecting solvolysis raw material cellulose acetate having the total substitution rate of acetyl of 1.5 to 3.0; and precipitating the cellulose acetate generated by deacetylation of the raw material cellulose acetate, in which the solvolysis of the raw material acetate cellulose proceeds at a temperature higher than a boiling temperature of the alcohol under the presence a solvent containing alcohol having three or smaller carbons and an acid catalyst.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to cellulose acetate and a method for producing cellulose acetate. [Background technology]

[0002] It is known that low-substituted cellulose acetate with a total acetyl substitution degree of 0.4 to 1.1 and water-soluble cellulose acetate with a total acetyl substitution degree of approximately 0.8 (low-substituted cellulose acetate) are metabolically decomposed by intestinal bacteria and exhibit physiological effects such as suppressing weight gain and reducing blood cholesterol (Patent Document 1 and Non-Patent Document 1).

[0003] The main metabolic degradation products of low-substituted cellulose acetate are acetic acid and propionic acid. Propionic acid is thought to be produced from glucose, which constitutes cellulose, via phosphoenolpyruvic acid and succinic acid (Non-Patent Documents 2 and 3). Acetic acid is thought to be produced by the release of acetic acid bound to cellulose in low-substituted cellulose acetate, and is also thought to be produced from glucose, which constitutes cellulose, via phosphoenolpyruvic acid (Non-Patent Documents 2 and 3).

[0004] Acetic acid and propionic acid, which are produced by intestinal bacteria through metabolic degradation of low-substituted cellulose acetate, are known to affect appetite and glucose metabolism by acting on nuclear receptors such as GPR43 in intestinal L cells to produce the incretin GLP-1 (Non-Patent Document 4), and also to act on the hypothalamus to suppress appetite, weight gain, and influence glucose and lipid metabolism (Non-Patent Document 5).

[0005] It is known that the enzyme acetyl xylan esterase is involved in the deacetylation of low-substituted cellulose acetate (Non-Patent Document 6). Note that Bacteroides xylanisolvens (Patent Document 1, Non-Patent Document 1), which grows in the intestines of rats fed low-substituted cellulose acetate, has been extensively studied as a xylan-degrading bacterium and is thought to possess acetyl xylan esterase. Based on these findings, it is presumed that the initial degradation in the metabolic degradation of low-substituted cellulose acetate by intestinal bacteria is deacetylation, and that acetyl xylan esterase is thought to be involved in this degradation.

[0006] Glucose, which is the main structural unit of cellulose, has hydroxyl groups at the 2-, 3-, and 6-positions. In low-substituted cellulose acetate, some of these hydroxyl groups are acetylated. Acetyl xylan esterase selectively removes the acetyl group at the 2- or 3-position, but hardly removes the acetyl group at the 6-position (Non-Patent Document 6). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6453851 [Non-patent literature]

[0008] [Non-Patent Document 1] Genda et al., Journal of Agricultural and Food Chemistry, 66, 11909-11916 (2018). [Non-patent document 2] Gijs den Besten et al., Journal of Lipid Research, 54, 2325-2340 (2013). [Non-patent document 3] Strobel, Applied and Environmental Microbiology, 58, 2331-2333 (1992). [Non-patent document 4] Sleeth et al., Nutrition Research Reviews, 23, 135-145 (2010). [Non-Patent Document 5] Frost et al., Nature Communications, DOI: 10.1038 (2014). [Non-patent document 6] Puls et al., Mactomolecular Symposia, 208, 239-253 (2004). [Non-Patent Document 7] Buchanan et al, Macromolecules, 24, 3060-3064 (1991). Summary of the Invention [Problem to be solved by the invention]

[0009] Low-substituted cellulose acetate is thought to exert its physiological effects through metabolic degradation by intestinal bacteria.Low-substituted cellulose acetate, which is biodegradable and susceptible to metabolic degradation by intestinal bacteria, is expected to exhibit excellent physiological effects.

[0010] Since acetyl xylan esterase rarely removes the acetyl group at the 6-position, in order to improve the biodegradability of low-substituted cellulose acetate, it is necessary to reduce the degree of acetyl substitution at the 6-position relative to the degrees of acetyl substitution at the 2- and 3-positions of the glucose ring of cellulose acetate.

[0011] However, conventional methods have not been able to reduce the degree of acetyl substitution at the 6-position of the glucose ring relative to the degrees of acetyl substitution at the 2- and 3-positions in cellulose acetate with a low total degree of acetyl substitution.

[0012] Furthermore, the more water-soluble a low-substituted cellulose acetate is, the more biodegradable it is. Therefore, low-substituted cellulose acetate with a low degree of acetyl substitution at the 6-position and excellent water solubility is particularly excellent in biodegradability.

[0013] However, such low-substituted cellulose acetates having a low degree of acetyl substitution at the 6-position and excellent water solubility have not been known until now. For example, the low-substituted cellulose acetate disclosed in Patent Document 1 does not have a low degree of acetyl substitution at the 6-position. Non-Patent Document 7 discloses low-substituted cellulose acetates with a low degree of acetyl substitution at the 6-position as Experiment No. 6 and Experiment No. 7, but these have poor water solubility.

[0014] An object of the present invention is to provide cellulose acetate having a low total degree of acetyl substitution, a low degree of acetyl substitution at the 6-position of the glucose ring relative to the degrees of acetyl substitution at the 2- and 3-positions, and excellent water solubility. [Means for solving the problem]

[0015] A first aspect of the present disclosure relates to cellulose acetate having a total degree of acetyl substitution of 0.4 to 0.9, a proportion of the degree of acetyl substitution at the 6-position in the total degree of acetyl substitution of 0% to 18%, and a light transmittance at 660 nm of a 4 wt% aqueous solution of cellulose acetate of 5% or more.

[0016] The cellulose acetate may have a light transmittance of 80% or more at 660 nm in a 4 wt % aqueous solution.

[0017] A second aspect of the present disclosure relates to a method for producing cellulose acetate, comprising the steps of deacetylating a starting cellulose acetate having a total degree of acetyl substitution of 1.5 to 3.0 by solvolysis, and precipitating the cellulose acetate produced by the deacetylation of the starting cellulose acetate, wherein the solvolysis of the starting cellulose acetate proceeds in the presence of a solvent containing an alcohol having 3 or less carbon atoms and an acid catalyst at a temperature equal to or higher than the boiling point of the alcohol.

[0018] In the method for producing cellulose acetate, the acid catalyst may have an acid dissociation constant pKa of 0 or less in water at 25°C.

[0019] In the method for producing cellulose acetate, the acid catalyst may be sulfuric acid.

[0020] In the method for producing cellulose acetate, the alcohol may be methanol.

[0021] In the method for producing cellulose acetate, the solvent may contain an acetate ester.

[0022] The method for producing cellulose acetate may include the steps of dissolving the precipitated cellulose acetate in water and removing residue, and precipitating the dissolved cellulose acetate.

[0023] The method for producing cellulose acetate may include the steps of dissolving the precipitated cellulose acetate in water and centrifuging to remove residue, and re-precipitating the dissolved cellulose acetate. [Effects of the Invention]

[0024] According to the present invention, it is possible to provide cellulose acetate having a low total degree of acetyl substitution, a low degree of acetyl substitution at the 6-position of the glucose ring relative to the degrees of acetyl substitution at the 2- and 3-positions, and excellent water solubility. DETAILED DESCRIPTION OF THE INVENTION

[0025] [Cellulose acetate] The cellulose acetate of the present disclosure has a total degree of acetyl substitution of 0.4 to 0.9, a proportion of the degree of acetyl substitution at the 6-position in the total degree of acetyl substitution of 0 to 18%, and a light transmittance of 660 nm of a 4 wt% aqueous solution of the cellulose acetate of the present disclosure of 5% or more.

[0026] [Total degree of acetyl substitution] The cellulose acetate of the present disclosure has a total acetyl substitution degree of 0.4 or more and 0.9 or less. When the total acetyl substitution degree is within this range, the cellulose acetate of the present disclosure has excellent water solubility and biodegradability. Note that the cellulose acetate of the present disclosure has a total acetyl substitution degree of 0.4 or more and 0.9 or less, and is sometimes referred to as low-substituted cellulose acetate.

[0027] [Acetyl substitution rate at 6-position] In the cellulose acetate of the present disclosure, the acetyl substitution degree at the 6-position of the total acetyl substitution degree is 0% or more and 18% or less, and the acetyl substitution degree at the 6-position is preferably 14% or less, and more preferably 10% or less. The acetyl substitution degree at the 6-position is most preferably 0%, but may be more than 0% and may be 4% or more. By having the acetyl substitution degree at the 6-position be 18% or less, the cellulose acetate is easily degradable by enzymes present in the intestine (e.g., acetyl xylan esterase) and is easily metabolized in the body.

[0028] The total degree of acetyl substitution and the proportion of the degree of acetyl substitution at the 6-position in the total degree of acetyl substitution can be determined by the following method.

[0029] First, the degree of acetyl substitution at the 2nd, 3rd, and 6th positions of the glucose ring of cellulose acetate is measured by NMR according to the method of Tezuka (Tezuka, Carbonydr. Res. 273, 83 (1995)). That is, the free hydroxyl groups of cellulose acetate are propionylated with propionic anhydride in pyridine. The obtained sample is dissolved in deuterated chloroform and 13 The C-NMR spectrum is measured. The carbon signals of the acetyl group appear in the region from 169 ppm to 171 ppm in the order of 2nd, 3rd, and 6th positions from the high magnetic field, and the signals of the carbonyl carbon of the propionyl group appear in the same order in the region from 172 ppm to 174 ppm. From the abundance ratio of the acetyl group and the propionyl group at each corresponding position, the degree of acetyl substitution at each of the 2nd, 3rd, and 6th positions of the glucose ring of cellulose acetate can be calculated. The degree of acetyl substitution can also be calculated as follows: 13 In addition to C-NMR, 1 It can also be analyzed by H-NMR.

[0030] The degree of acetyl substitution at the i-position is the molar number of acetyl groups at the i-position divided by the sum of the molar number of acetyl groups at the i-position and the molar number of hydroxyl groups, and is a real number between 0 and 1. Here, i is 2, 3, or 6. The total degree of acetyl substitution is the sum of the degrees of acetyl substitution at the 2-, 3-, and 6-positions of the glucose ring of cellulose acetate. The proportion (%) of the degree of acetyl substitution at the 6-position in the sum of the degrees of acetyl substitution at the 2-, 3-, and 6-positions of the glucose ring of cellulose acetate is the proportion of the degree of acetyl substitution at the 6-position in the total degree of acetyl substitution.

[0031] The total degree of acetyl substitution can be converted into the degree of acetylation using the following formula. DS=162.14×AV×0.01 / (60.052-42.037×AV×0.01) DS: Total degree of acetyl substitution AV: Acetyl content (%)

[0032] [Light transmittance] The cellulose acetate according to the present disclosure has a light transmittance at 660 nm of 5% or more in a 4 wt% aqueous solution of the cellulose acetate, preferably 10% or more, more preferably 30% or more, even more preferably 50% or more, and most preferably 80% or more. The light transmittance may be 99% or less, 98% or less, or 95% or less. If the light transmittance at 660 nm in a 4 wt% aqueous solution is less than 5%, the cellulose acetate has poor water solubility.

[0033] The light transmittance at 660 nm of a 4 wt % aqueous solution of cellulose acetate can be determined using a spectrophotometer (Shimadzu Corporation, ultraviolet-visible spectrophotometer UV-1800, cell material: polystyrene, cell length: 10 mm).

[0034] [Degree of polymerization (viscosity average degree of polymerization)] The viscosity-average degree of polymerization of the cellulose acetate of the present disclosure is not particularly limited, but is preferably from 3 to 400, more preferably from 10 to 200, and even more preferably from 15 to 150. When the viscosity-average degree of polymerization is within this range, the cellulose acetate exhibits particularly excellent water solubility and biodegradability.

[0035] The viscosity-average degree of polymerization (DP) can be evaluated as the viscosity-average degree of polymerization based on the intrinsic viscosity ([η], unit: g / ml) as shown below. Specifically, the intrinsic viscosity is determined by a method in accordance with JIS-K-7367-1 and ISO1628-1, the viscosity-average molecular weight is calculated according to the literature by Kamide et al., and the viscosity-average degree of polymerization can be calculated from the viscosity-average molecular weight.

[0036] The cellulose acetate of the present disclosure can be produced by the following production method.

[0037] The cellulose acetate of the present disclosure has a low total degree of acetyl substitution, and a lower degree of acetyl substitution at the 6-position of the glucose ring compared to the 2- and 3-positions. Therefore, it is highly degradable by enzymes present in the intestine (e.g., acetyl xylan esterase, etc.), is easily metabolized in the body, and can be used as a food product.

[0038] [Method of manufacturing cellulose acetate] The method for producing cellulose acetate disclosed herein comprises the steps of deacetylating a starting cellulose acetate having a total degree of acetyl substitution of 1.5 to 3.0 by solvolysis, and precipitating the cellulose acetate produced by deacetylation of the starting cellulose acetate, wherein the solvolysis of the starting cellulose acetate proceeds in the presence of a solvent containing an alcohol having 3 or less carbon atoms and an acid catalyst at a temperature equal to or higher than the boiling point of the alcohol.

[0039] [Deacetylation step] In the deacetylation step in the method for producing cellulose acetate of the present disclosure, starting cellulose acetate is subjected to solvolysis. In the deacetylation step of the present disclosure, deacetylation proceeds by solvolysis. The solvolysis may involve only a solvent containing an alcohol having 3 or fewer carbon atoms, or may involve a solvent containing an alcohol having 3 or fewer carbon atoms and other solvents such as water. Solvolysis also includes hydrolysis.

[0040] (Raw cellulose acetate) As the starting cellulose acetate, cellulose acetate with a medium to high degree of substitution can be used. The total acetyl substitution degree of the medium to high acetyl substitution cellulose acetate used as the starting material is 1.5 to 3.0, preferably 1.5 to 2.5. As the starting cellulose acetate, commercially available cellulose diacetate (total acetyl substitution degree 2.20 to 2.56) or cellulose triacetate (total acetyl substitution degree greater than 2.56 to 3) can be used.

[0041] The starting cellulose acetate may be produced by a conventionally known production method. For example, it can be produced through a series of steps including a step of disintegrating pulp, which is a cellulose material, a step of pretreatment, a step of acetylation, a step of hydrolysis, a step of precipitation, and a step of adding a stabilizer. Each of these steps will be explained below. For a general method of producing cellulose acetate, see "Wood Chemistry" (vol. 1) (Migita et al., Kyoritsu Shuppan Co., Ltd., 1968, pp. 180-190).

[0042] The α-cellulose content of the pulp is preferably 92% by weight or more, more preferably 93% by weight or more, and even more preferably 94% by weight or more. There is no particular upper limit, but it may be 99% by weight or less. Such high-purity pulp contains almost no wood-derived lignin and also little hemicellulose. This is because the amount of these impurities is low, making it possible to obtain cellulose acetate, which is particularly water-soluble and biodegradable.

[0043] The α-cellulose content can be determined as follows: A known weight of pulp is extracted successively with 17.5% and 9.45% aqueous sodium hydroxide solutions at 25°C, the soluble portion of the extract is oxidized with potassium dichromate, and the weight of β,γ-cellulose is determined from the volume of potassium dichromate required for oxidation. The weight of the insoluble portion of the pulp, or α-cellulose, is determined by subtracting the weight of β,γ-cellulose from the initial weight of the pulp (TAPPI T203). The ratio of the weight of the insoluble portion of the pulp to the initial weight of the pulp is the α-cellulose content (wt%).

[0044] As the pulp, wood pulp (softwood pulp, hardwood pulp), cotton linter, etc. These celluloses may be used alone or in combination of two or more kinds, for example, softwood pulp may be used in combination with cotton linter or hardwood pulp.

[0045] Wood pulp is preferred because it is available as a stable raw material and is more cost-effective than linter. Examples of wood pulp include hardwood pre-hydrolyzed kraft pulp.

[0046] In the step of crushing the pulp, for example, the pulp can be crushed in a dry manner using a disc refiner.

[0047] In the pretreatment step, the disintegrated pulp is brought into contact with acetic acid or sulfur-containing acetic acid. The acetic acid to be used may be 96 to 100% by weight, and the sulfur-containing acetic acid is acetic acid containing sulfuric acid, preferably containing 1 to 10% by weight of sulfuric acid.

[0048] In the acetylation step, the pretreated pulp is brought into contact with a mixed solution of acetic acid and acetic anhydride to acetylate the pulp with acetic anhydride, thereby obtaining fully tri-substituted cellulose acetate (primary cellulose acetate). The mixed solution preferably contains sulfuric acid as a catalyst. In the acetylation step, 96 to 100 wt % acetic acid can be used, and concentrated sulfuric acid is preferred.

[0049] In the hydrolysis step, a neutralizing agent such as water, dilute acetic acid, or magnesium acetate aqueous solution is added to neutralize the sulfuric acid (complete or partial neutralization) and inactivate the acetic anhydride, thereby terminating the acetylation reaction. This hydrolyzes the fully trisubstituted cellulose acetate (primary cellulose acetate) to obtain a cellulose acetate (secondary cellulose acetate) with the desired degree of substitution. Here, dilute acetic acid refers to an aqueous solution of acetic acid with a concentration of 1 to 50% by weight. The magnesium acetate concentration of the aqueous magnesium acetate solution is preferably 5 to 30% by weight.

[0050] In the precipitation step, a mixture containing cellulose acetate is mixed with a precipitant such as water, dilute acetic acid, a dilute aqueous solution of calcium hydroxide, or an aqueous solution of magnesium acetate to precipitate cellulose acetate. The resulting cellulose acetate (precipitate) is then separated and washed with water to remove free metal components, sulfuric acid components, etc.

[0051] In the step of adding a stabilizer, in addition to washing with water, an alkali metal compound and / or an alkaline earth metal compound, particularly a calcium compound such as calcium hydroxide, may be added as a stabilizer as needed. The stabilizer may also be used during washing with water.

[0052] (Solvolysis of raw cellulose acetate) The solvolysis of the starting cellulose acetate proceeds in the presence of a solvent containing an alcohol having 3 or less carbon atoms and an acid catalyst at a temperature equal to or higher than the boiling point of the alcohol.

[0053] The solvent containing an alcohol having 3 or less carbon atoms may be any solvent that contains an alcohol having 3 or less carbon atoms and is capable of dissolving the starting cellulose acetate. "Able to dissolve the starting cellulose acetate" means that the starting cellulose acetate can be molecularly dispersed in part or in whole, either with or without heating, and that a clear change or disappearance in the morphology of the solid starting cellulose acetate can be visually observed.

[0054] The alcohol having 3 or less carbon atoms contained in the solvent is not particularly limited. Examples include methanol, ethanol, 1-propanol, and 2-propanol. Among these, methanol and ethanol are preferred, and methanol is more preferred.

[0055] The content of the alcohol having 3 or less carbon atoms in the solvent is preferably 70% by weight or more, more preferably 80% by weight or more, and may be 100% by weight or less.

[0056] The solvent may contain optional components such as acetate esters, acetic acid, and acetone in addition to the alcohol having 3 or less carbon atoms. Among these, acetate esters are preferred, and among acetate esters, ethyl acetate and methyl acetate are more preferred. This is because they increase the solubility of the starting material (cellulose acetate raw material) and / or reaction intermediates in the reaction bath, thereby producing cellulose acetate with excellent water solubility and biodegradability.

[0057] The content of optional components other than the alcohol having 3 or less carbon atoms in the solvent is preferably 30% by weight or less, and more preferably 20% by weight or less. In particular, when an acetate ester is contained as an optional component, the content of the acetate ester in the solvent is preferably 10% by weight or more and 5% by weight or less.

[0058] The amount of the solvent containing an alcohol having 3 or less carbon atoms used is, for example, 0.5 to 50 parts by weight, preferably 1 to 20 parts by weight, and more preferably 3 to 10 parts by weight, per part by weight of the raw material cellulose acetate.

[0059] The catalyst may be an acid catalyst generally used as a deacetylation catalyst. Examples of the acid catalyst include inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid; and organic acids such as trifluoroacetic acid and formic acid. These acid catalysts may be used alone or in combination of two or more.

[0060] The acid catalyst preferably has an acid dissociation constant pKa of 0 or less, more preferably -0.5 or less, and even more preferably -1.0 or less in water at 25°C. The acid dissociation constant pKa may be -6.0 or more.

[0061] The acid catalyst is preferably sulfuric acid. Concentrated sulfuric acid, such as an aqueous solution of sulfuric acid with a sulfuric acid concentration of 98% by weight, can be used. The catalyst may be mixed in advance with a solvent containing an alcohol having 3 or less carbon atoms and used for the solvolysis of the starting cellulose acetate.

[0062] The amount of acid catalyst used is, for example, preferably 0.005 to 1 part by weight, more preferably 0.01 to 0.5 parts by weight, and even more preferably 0.02 to 0.3 parts by weight, per part by weight of the starting cellulose acetate. If the amount of catalyst is too small, the solvolysis time becomes too long, which is economically undesirable, despite the advantage of making it easier to control the reaction endpoint. On the other hand, if the amount of catalyst is too large, the degree of change in the depolymerization rate relative to the solvolysis temperature increases, making it difficult to control the reaction endpoint, and making it difficult to obtain cellulose acetate having the total degree of substitution described in the present disclosure. Furthermore, the resulting cellulose acetate is likely to be non-uniform, with varying degrees of acetyl substitution.

[0063] The water content in the solvolysis reaction system is preferably as low as possible, preferably 2 parts by weight or less, more preferably 1 part by weight or less, and even more preferably 0.5 parts by weight or less, per part by weight of the starting cellulose acetate. There is no lower limit to the water content in the solvolysis reaction system, as long as the solvolysis of the starting cellulose acetate is initiated and progresses, but the water content may be, for example, 0.01 part by weight or more per part by weight of the starting cellulose acetate.

[0064] When subjecting the starting cellulose acetate to solvolysis, the water originally contained in the starting cellulose acetate may or may not be removed in advance. The water content of the starting cellulose acetate may be, for example, 5% by weight or less, 4% by weight or less, or 3% by weight or less, or 1% by weight or more.

[0065] The moisture content of raw cellulose acetate can be measured using the following method. It can be measured using a Kett moisture meter (METTLER TOLEDO HB43). Approximately 2.0 g of a wet sample is placed on the aluminum pan of the Kett moisture meter and heated at 120°C until the weight no longer changes. The moisture content (wt%) of the sample can be calculated from the change in weight before and after heating.

[0066] In the step of deacetylating the starting cellulose acetate by solvolysis, water may be added to the system in addition to the water originally contained in the starting cellulose acetate. All of the water may be present in the system at the start of the reaction, or a portion of the water to be used may be present in the system at the start of the reaction, and the remaining water may be added to the system in one or several divided portions.

[0067] The content of water in the solvolysis reaction system is preferably 20 parts by weight or less, more preferably 10 parts by weight or less, and even more preferably 5 parts by weight or less, per part by weight of the solvent.

[0068] The temperature in the solvolysis reaction system is adjusted to a temperature equal to or higher than the boiling point of the alcohol having 3 or fewer carbon atoms. For example, when methanol is used as the alcohol having 3 or fewer carbon atoms, the temperature is 65°C or higher, when ethanol is used, 78°C or higher, when 1-propanol is used, 97°C or higher, and when 2-propanol is used, 82°C or higher. The starting cellulose acetate can be sufficiently dissolved in the solvent, allowing the solvolysis reaction to proceed uniformly.

[0069] The temperature in the solvolysis reaction system is not limited as long as it is equal to or higher than the boiling point of the alcohol having 3 or less carbon atoms, but is preferably equal to or lower than 105° C., more preferably equal to or lower than 100° C., and even more preferably equal to or lower than 95° C. If the temperature exceeds 105° C., the degree of polymerization of the resulting cellulose acetate and the yield will decrease significantly.

[0070] The gauge pressure in the solvolysis reaction system is preferably 0.2 MPaG or more and 1 MPaG or less. It is preferably 0.2 MPaG or more and 0.7 MPaG or less, and more preferably 0.2 MPaG or more and 0.5 MPaG or less. By setting the pressure to 0.2 MPaG or more, the starting cellulose acetate can be sufficiently dissolved in the solvent, allowing the solvolysis reaction to proceed particularly uniformly. If the pressure exceeds 1 MPaG, the degree of polymerization of the resulting cellulose acetate and the yield will decrease significantly.

[0071] The solvolysis reaction time may be from 20 to 300 minutes, from 30 to 240 minutes, or from 60 to 200 minutes. By keeping the time within this range, it is easy to adjust the total degree of acetyl substitution to from 0.4 to 0.9.

[0072] Here, the solvolysis reaction time refers to the time during which the temperature is maintained after the temperature in the solvolysis reaction system is reached.

[0073] In conventional deacetylation of raw cellulose acetate, the raw cellulose acetate is dissolved in a mixed solvent of acetic acid and water and hydrolyzed using a sulfuric acid catalyst. During this process, acetyl group elimination proceeds roughly equally at the 2-, 3-, and 6-positions of the glucose ring of cellulose acetate. In contrast, in the method for producing cellulose acetate disclosed herein, the acetyl group at the 6-position is preferentially eliminated, resulting in cellulose acetate with a lower degree of acetyl substitution at the 6-position than at the 2- and 3-positions of the glucose ring.

[0074] In conventional deacetylation of cellulose acetate as a starting material, acetic acid is used as a reaction solvent. During the deacetylation process, the reaction proceeds while acetic acid is preferentially reacetylated at the 6-position. Therefore, the apparent elimination of acetyl groups occurs equally at the 2-, 3-, and 6-positions of the glucose ring of cellulose acetate. Cellulose acetate with a low degree of substitution at the 6-position can be obtained by suppressing reacetylation at the 6-position, but in this case, a solvent to replace acetic acid is required. After extensive investigation, the present inventors have found that solvents containing alcohols having 3 or fewer carbon atoms are suitable as reaction solvents above their boiling points for this purpose. Solvents containing alcohols having 3 or fewer carbon atoms dissolve or highly swell the starting cellulose acetate with a medium to high degree of substitution above their boiling points.

[0075] The solvolysis of the starting cellulose acetate can be terminated by the addition of a neutralizing agent. Examples of neutralizing agents include salts of weak acids, such as acetates (e.g., sodium acetate and magnesium acetate) and carbonates (e.g., sodium carbonate and magnesium carbonate). The neutralizing agent may be added together with a solvent containing an alcohol having 3 or fewer carbon atoms.

[0076] The amount of neutralizing agent used may be 1.0 to 5.0 equivalents, preferably 1.1 to 3.0 equivalents, and more preferably 1.2 to 2.0 equivalents, per equivalent of the acid catalyst. If the amount of neutralizing agent is too small, the acid catalyst may remain in the low-substituted cellulose acetate, causing decomposition of the low-substituted cellulose acetate. On the other hand, if the amount of neutralizing agent is too large, a large amount of solvent will be used to wash off the neutralizing agent, which is economically undesirable.

[0077] [Precipitation process] In the precipitation step in the method for producing cellulose acetate according to the present disclosure, the cellulose acetate produced by deacetylation of the starting cellulose acetate is precipitated.

[0078] An example of a precipitation method is to precipitate cellulose acetate with a low degree of substitution by cooling the reaction system to room temperature after the completion of the solvolysis reaction of the starting cellulose acetate. This precipitation method using cooling does not require the addition of a precipitation solvent and is therefore economically preferable. However, the addition of a precipitation solvent may be acceptable, since it may promote the precipitation of cellulose acetate with a low degree of substitution and increase the yield.

[0079] Examples of the precipitation solvent include solvents containing the alcohols having 3 or less carbon atoms; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate and methyl acetate; nitrogen-containing compounds such as acetonitrile; ethers such as tetrahydrofuran; and mixed solvents thereof. These precipitation solvents may be used alone, or mixed solvents containing two or more solvents may be used. Among these, solvents containing the alcohols having 3 or less carbon atoms are preferred because using the same solvent as the reaction solvent as the precipitation solvent can facilitate the recovery and reuse of waste solvents.

[0080] The precipitation solvent preferably contains the following basic substance, since neutralization can be carried out simultaneously with precipitation.

[0081] [Optional process] (Cleaning process, neutralization process) The precipitated cellulose acetate is preferably washed with an organic solvent (poor solvent) such as an alcohol such as methanol or a ketone such as acetone. It is also preferable to wash and neutralize it with an organic solvent containing a salt of a weak acid or a basic substance (e.g., an alcohol such as methanol, a ketone such as acetone, etc.). By washing and neutralization, impurities such as the catalyst (e.g., sulfuric acid) used in the solvolysis step can be efficiently removed.

[0082] Examples of the salts of weak acids include acetates such as sodium acetate and magnesium acetate, and carbonate acetate hydrates such as sodium carbonate and magnesium carbonate. Examples of the basic substance that can be used include alkali metal compounds such as alkali metal hydroxides such as calcium hydroxide.

[0083] (purification process) The precipitated cellulose acetate can be further purified to obtain cellulose acetate with excellent water solubility. In particular, the higher the total degree of acetyl substitution of the starting cellulose acetate, the lower the water solubility of the resulting cellulose acetate tends to be, so purification is preferred. Purification can be carried out, for example, by precipitation fractionation (fractional precipitation) and / or dissolution fractionation (fractional dissolution).

[0084] Dissolution fractionation can be carried out, for example, by dissolving the precipitated cellulose acetate (solid) in water or a mixed solvent of water and a hydrophilic organic solvent (e.g., acetone) to prepare an aqueous solution, and then removing the residue (i.e., insoluble components). Centrifugal separation may be used as a method for removing the residue.

[0085] The cellulose acetate can be dissolved by stirring at an appropriate temperature (for example, 20 to 80°C, preferably 25 to 60°C). The concentration (blending ratio) of the cellulose acetate in the aqueous solution can be adjusted to an appropriate concentration (for example, 2 to 10% by weight, preferably 3 to 8% by weight).

[0086] When the mixed solvent of water and a hydrophilic organic solvent is used, the concentration of the organic solvent in the mixed solvent may be, for example, 5 to 50% by weight, and preferably 10 to 40% by weight.

[0087] After removing the residue, the dissolved cellulose acetate can be precipitated. Precipitation methods include reprecipitation and spray drying. Precipitation solvents used for reprecipitation include solvents containing the above-mentioned alcohols having 3 or less carbon atoms; ketones such as acetone and methyl ethyl ketone; esters such as ethyl acetate and methyl acetate; nitrogen-containing compounds such as acetonitrile; ethers such as tetrahydrofuran; and mixed solvents thereof. These precipitation solvents may be used alone, or mixed solvents containing two or more solvents may be used.

[0088] (stabilizer added) After precipitation of cellulose acetate, a stabilizer may be added to the precipitated cellulose acetate to enhance the thermal stability of the cellulose acetate. Preferred stabilizers are alkali metal compounds and / or alkaline earth metal compounds, particularly calcium compounds such as calcium hydroxide.

[0089] The amount of stabilizer added is preferably, for example, a volume ratio of 100:1-10 between the reaction mixture containing cellulose acetate and an aqueous calcium hydroxide solution adjusted to 0.2-1.0 wt %.

[0090] The stabilizer may be added at the same time as removing free metal components, sulfuric acid components, etc. by washing the precipitate with a poor solvent such as the precipitating solvent.

[0091] After the step of precipitating the deacetylated cellulose acetate, or after any optional step if the method includes such an optional step, it is preferable to dry the cellulose acetate. When drying the cellulose acetate, the drying method is not particularly limited, and a conventionally known drying method can be used. Examples include air drying such as hot air drying, reduced pressure drying, and vacuum drying. The temperature and pressure may be adjusted as appropriate.

[0092] After drying, the cellulose acetate may be pulverized. For pulverization, a conventional pulverizer such as a sample mill, hammer mill, turbo mill, atomizer, cutter mill, bead mill, ball mill, roll mill, jet mill, or pin mill may be used. Furthermore, freeze pulverization, dry pulverization at room temperature, or wet pulverization may also be used. [Example]

[0093] The present invention will be specifically explained below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0094] <Preparation and properties of cellulose acetate> For the cellulose acetates of the Examples and Comparative Examples, the physical properties shown in Table 1 were measured as follows.

[0095] (Reaction product yield) The reaction product yield (yield of cellulose acetate before the purification step) (% by weight) was calculated as follows. Reaction product yield (wt%) = Actual yield of solvolysis reaction product (cellulose acetate before purification if a purification step is included) / Theoretical yield of solvolysis reaction product (cellulose acetate before purification if a purification step is included)

[0096] (Purified product yield) The yield of the purified product (wt%) was calculated as follows. Yield of purified product (yield of cellulose acetate after purification step) (wt%) = Actual yield of purified product (cellulose acetate after purification step if purification step is included) / Actual yield of solvolysis reaction product (cellulose acetate before purification step if purification step is included)

[0097] (Total degree of acetyl substitution, degree of acetyl substitution at 2-, 3-, and 6-positions (DS2, DS3, and DS6), and ratio of degree of acetyl substitution at 6-position to total degree of acetyl substitution) According to the literature of Tezuka et al. (Carbohydrate Research, 273, 83-91 (1995)), the sample was propionylated with propionic anhydride in pyridine solvent, and then dehydrated with chloroform solvent. 13 The C-NMR spectrum was measured, and the intensities of three signals of acetyl carbon appearing around 169.1 to 170.2 ppm were integrated, and the intensities of three signals of propionyl carbon appearing around 172.7 to 173.6 ppm were integrated.

[0098] 13 In the C-NMR spectrum, the three acetyl carbonyl carbon signals appearing around 169.1 to 170.2 ppm are assigned to the 2nd, 3rd, and 6th positions, respectively, from the high magnetic field side. The intensity of each signal was integrated within a range of ±0.2 ppm from the maximum, and this was defined as the integrated intensity of each acetyl carbonyl carbon signal. The DS i (i is 2, 3 or 6). DS i=DS × (integrated intensity of acetyl carbonyl carbon signal at i-position) / (sum of integrated intensities of acetyl carbonyl carbon signals at 2-, 3-, and 6-positions)

[0099] The NMR measurement conditions are as follows: Measurement solvent: CDCl3 (approximately 3 ml) Measurement temperature: 40℃ Sample amount: 160-180mg (φ10mm) Observed nucleus: 13C (1H fully decoupled) Number of data points: 32768 Pulse angle and time: 45°, 9μsec Data acquisition time: 0.9667 seconds Waiting time: 2.0333 seconds Accumulation count: 18,000 times

[0100] The total degree of acetyl substitution (DS) was calculated by the following formula, where X is the integrated intensity of the acetyl carbonyl carbon signal and Y is the integrated intensity of the propionyl carbonyl carbon signal. Total degree of acetyl substitution (DS) = 3 x [X / (X+Y)]

[0101] The ratio (%) of the degree of acetyl substitution at the 6-position to the total degree of acetyl substitution was calculated using the following formula. Percentage of acetyl substitution at 6-position (%) = acetyl substitution at 6-position (DS6) / total acetyl substitution (DS) × 100

[0102] (Degree of polymerization (viscosity average degree of polymerization)) The degree of polymerization of cellulose acetate was evaluated as the viscosity-average degree of polymerization based on the intrinsic viscosity number ([η], unit: g / ml).

[0103] Specifically, first, the intrinsic viscosity of cellulose acetate was determined in accordance with JIS-K-7367-1 and ISO1628-1, using a size 1C Ubbelohde viscometer as a viscometer and dimethyl sulfoxide (DMSO) as a solvent, based on the value obtained by dividing the logarithmic relative viscosity at 25°C by the concentration.

[0104] Next, the molecular weight (viscosity average molecular weight) of cellulose acetate was calculated using the following formula according to the literature by Kamide et al. Viscosity average molecular weight = (intrinsic viscosity number [η] / 0.171) (1 / 0.61)

[0105] The degree of polymerization (viscosity average degree of polymerization) of cellulose acetate was calculated using the following formula: Degree of polymerization (viscosity average degree of polymerization) = viscosity average molecular weight / (162.14+42.037×DS)

[0106] (Transmittance (4wt% aqueous solution transmittance)) 0.4 g of cellulose acetate was dispersed in 10 ml of water, stirred for 2 hours with a magnetic stirrer, allowed to stand overnight, and stirred again for 2 hours. The transmittance (%) of the resulting 4% aqueous solution of cellulose acetate at 660 nm was measured using a spectrophotometer (Shimadzu Corporation, UV-1800 UV-Visible Spectrophotometer, cell material: polystyrene, cell length: 10 mm).

[0107] (Example A-1) Deacetylation step: As a starting cellulose acetate, 70 parts by weight of cellulose diacetate (manufactured by Daicel Corporation, trade name "L-50", water content 3% by weight, total acetyl substitution degree 2.43, acetyl substitution degree at 2-position 0.86, acetyl substitution degree at 3-position 0.82, acetyl substitution degree at 6-position 0.75) was added to 554 parts by weight of methanol as a solvent at room temperature, and 3.5 parts by weight of sulfuric acid as a catalyst was further added. The mixture was heated to 90°C over a period of 50 minutes with stirring, and then maintained at 90°C for 100 minutes.

[0108] Precipitation step: The reaction mixture was cooled to room temperature, and a mixture of 14.6 parts by weight of sodium acetate trihydrate and 55 parts by weight of methanol was added to neutralize the sulfuric acid. The white solid suspended in the reaction mixture was separated by suction filtration. The separated white solid was suspended in 277 parts by weight of methanol and stirred at room temperature for 1 hour. The white solid in the methanol was separated by suction filtration.

[0109] The filtered white solid was suspended again in 277 parts by weight of methanol and stirred at room temperature for 1 hour. The white solid in methanol was filtered off by suction filtration. The white solid washed with methanol was dried under reduced pressure at 60°C until it reached a constant weight, yielding 60 parts by weight of low-substituted cellulose acetate. The physical properties of the obtained low-substituted cellulose acetate were measured and the results are shown in Table 1.

[0110] (Example A-2) Deacetylation and Precipitation Steps: In the same manner as in Example A-1, 60 parts by weight of low-substituted cellulose acetate was obtained.

[0111] Purification process: This low-substituted cellulose acetate was then added to 1,440 parts by weight of water, stirred at room temperature for 8 hours, and allowed to stand overnight. The suspension was centrifuged at 12,600 G for 30 minutes to obtain a supernatant. This supernatant was added dropwise to 10,000 parts by weight of acetone with stirring to obtain a white precipitate. This white precipitate was filtered by suction and dried under reduced pressure at 60°C until a constant weight was reached, yielding 54 parts by weight of low-substituted cellulose acetate. The physical properties of the obtained low-substituted cellulose acetate were measured and the results are shown in Table 1.

[0112] (Example A-3) Deacetylation and Precipitation Steps: Cellulose acetate manufactured by Eastman Chemical Company (trade name "CA-320S", moisture content 3% by weight, total acetyl substitution degree 1.80, degree of 2-acetyl substitution 0.61, degree of 3-acetyl substitution 0.56, degree of 6-acetyl substitution 0.63) was used instead of cellulose diacetate (manufactured by Daicel Corporation, trade name "L-50", moisture content 3% by weight), and the temperature setting time at 90°C was changed to 80 minutes in the same manner as in Example A-1, to obtain 68 parts by weight of low-substituted cellulose acetate. The physical properties of the obtained low-substituted cellulose acetate were measured, and the results are shown in Table 1.

[0113] (Comparative example A-1) Deacetylation step: As the starting cellulose acetate, 100 parts by weight of cellulose diacetate (manufactured by Daicel Corporation, trade name "L-50", water content 3% by weight, total acetyl substitution degree 2.43, 2-position acetyl substitution degree 0.86, 3-position acetyl substitution degree 0.82, 6-position acetyl substitution degree 0.75) was added to a mixture of 358 parts by weight of acetic acid and 95 parts by weight of water (mixed solvent) as a solvent, and the mixture was stirred at 70°C for 5 hours and then allowed to stand overnight at room temperature (approximately 25°C). The mixture was then heated to 70°C, and 178 parts by weight of water was added to obtain a cellulose diacetate solution.

[0114] The cellulose diacetate solution was heated to 50°C, and a mixture of 12.6 parts by weight of 98% sulfuric acid (catalyst) and 57 parts by weight of acetic acid (solvent) was added. The reaction mixture was heated to 50°C with stirring, and 4 hours after the addition of sulfuric acid, 137 parts by weight of water was added over 30 minutes, and 8 hours after the addition of sulfuric acid, 111 parts by weight of water was added over 30 minutes. The reaction mixture was continued to be heated to 50°C with stirring, and 23 hours and 40 minutes (1,420 minutes) after the addition of sulfuric acid, a mixture of 72 parts by weight of sodium acetate trihydrate and 109 g of water was added to quench the reaction.

[0115] Precipitation step: This reaction mixture was added dropwise to 4,700 parts by weight of methanol with stirring to obtain a white precipitate. This white precipitate was filtered, dispersed in 1,100 parts by weight of methanol, and filtered again. This procedure was repeated five times. The filtered white precipitate was dried under reduced pressure at 60°C until it reached a constant weight, yielding 64 parts by weight of low-substituted cellulose acetate. The physical properties of the obtained low-substituted cellulose acetate were measured and the results are shown in Table 1.

[0116] (Comparative example A-2) Low-substituted cellulose acetate was obtained by a method according to Example 17 of Japanese Patent No. 6378712. Specifically, the method is as follows.

[0117] Deacetylation step: A mixture of 510 parts by weight of acetic acid and 95 parts by weight of water was added to 100 parts by weight of cellulose diacetate (manufactured by Daicel Corporation, trade name "L-50," water content 3 wt%, total acetyl substitution degree 2.43, acetyl substitution degree at 2-position 0.86, acetyl substitution degree at 3-position 0.82, acetyl substitution degree at 6-position 0.75), and the mixture was stirred at 70°C for 3 hours to obtain a cellulose diacetate solution. This cellulose diacetate solution was then heated to 70°C with stirring, and 13 parts by weight of 98% sulfuric acid was added. The reaction mixture was then heated to 70°C with continued stirring. 3 hours after the addition of sulfuric acid, 67 parts by weight of water was added over 5 minutes, and 8 hours after the addition of sulfuric acid, 133 parts by weight of water was added over 10 minutes. The reaction mixture was then heated to 70°C with continued stirring, and 10 hours (600 minutes) after the addition of sulfuric acid, the reaction mixture was cooled to 25°C to essentially stop the reaction.

[0118] Precipitation step: The reaction mixture was added dropwise to 1,500 parts by weight of acetone with stirring, yielding a white precipitate. This white precipitate was filtered, dispersed in 800 parts by weight of acetone, and filtered again, three times. This filtered white precipitate was dispersed in 800 parts by weight of methanol containing 0.004% by weight of potassium acetate, and filtered again, two times. The filtered white precipitate was dried under reduced pressure at 60°C until it reached a constant weight. 960 parts by weight of a 20% by weight aqueous acetone solution was added to 64 parts by weight of this dried product, and the mixture was stirred at 40°C for 8 hours. After the concentrated phase was removed by centrifugation, parts by weight of acetone was added to the diluted phase, yielding a white precipitate. This white precipitate was filtered, dispersed in 3,000 parts by weight of acetone, and filtered again. The filtered white precipitate was dried under reduced pressure at 60°C until it reached a constant weight, yielding 59 parts by weight of low-substituted cellulose acetate. The physical properties of the obtained low-substituted cellulose acetate were measured and the results are shown in Table 1.

[0119] (Comparative example A-3) Low-substituted cellulose acetate was obtained according to the conditions of experiment number 6 in Edgar et al., Macromolecules, 24, 3060 (1991).

[0120] Specifically, 60 parts by weight of cellulose diacetate (manufactured by Daicel Corporation, trade name "L-50," dried under reduced pressure at 60°C until a constant weight was reached) was suspended in 237 parts by weight of methanol, 0.2 parts by weight of molybdenum hexacarbonyl (Mo(CO)6) was added, and the internal pressure was adjusted to 200 psi using nitrogen in a sealed reactor, followed by heating at 140°C for 7 hours (420 minutes). The reaction mixture was cooled to room temperature, and the solid was filtered off by suction filtration. The filtered solid was dried under reduced pressure at 60°C until a constant weight was reached, yielding 29 parts by weight of low-substituted cellulose acetate. The physical properties of the obtained low-substituted cellulose acetate were measured, and the results are shown in Table 1.

[0121] (Comparative example A-4) Low-substituted cellulose acetate was obtained according to the conditions of experiment number 7 in Edgar et al., Macromolecules, 24, 3060 (1991).

[0122] Specifically, 60 parts by weight of cellulose diacetate (manufactured by Daicel Corporation, trade name "L-50," dried under reduced pressure at 60°C until a constant weight was reached) was suspended in 237 parts by weight of methanol, 0.2 parts by weight of molybdenum(VI) oxide (MoO) was added, and the internal pressure was adjusted to 1,000 psi using nitrogen in a sealed reactor, followed by heating at 155°C for 3 hours (180 minutes). The reaction mixture was cooled to room temperature, and the solid was filtered off by suction filtration. The filtered solid was dried under reduced pressure at 60°C until a constant weight was reached, yielding 37 parts by weight of low-substituted cellulose acetate. The physical properties of the obtained low-substituted cellulose acetate were measured, and the results are shown in Table 1.

[0123] [Table 1]

[0124] The cellulose acetate of Comparative Example A-1 had a degree of acetyl substitution at the 6-position of 0.24, and the proportion of the degree of acetyl substitution at the 6-position in the total degree of acetyl substitution was 36.9%. The cellulose acetate of Comparative Example A-2 had a degree of acetyl substitution at the 6-position of 0.28, and the proportion of the degree of acetyl substitution at the 6-position in the total degree of acetyl substitution was 35.9%. In the cellulose acetates of Comparative Examples A-1 and A-2, the degree of acetyl substitution at the 6-position was higher than the degrees of acetyl substitution at the 2- and 3-positions.

[0125] The cellulose acetate of Comparative Example A-3 had a degree of acetyl substitution at the 6-position of 0.05, and the proportion of the degree of acetyl substitution at the 6-position in the total degree of acetyl substitution was 10.4%, while the cellulose acetate of Comparative Example A-4 had a degree of acetyl substitution at the 6-position of 0.06, and the proportion of the degree of acetyl substitution at the 6-position in the total degree of acetyl substitution was 12.0%, meaning that the cellulose acetates of Comparative Examples A-3 and A-4 had a lower degree of acetyl substitution at the 6-position than the acetyl substitution at positions 2 and 3. However, a 4 wt% aqueous solution had a low light transmittance at 660 nm, and the cellulose acetates were poorly water-soluble.

[0126] On the other hand, the cellulose acetates of Examples A-1 to A-3 have a low acetyl substitution degree at the 6-position relative to the total acetyl substitution degree of 18% or less, and a 4 wt% aqueous solution has a light transmittance at 660 nm of 5% or more, indicating excellent water solubility. In particular, the cellulose acetates of Examples A-2 and A-3 have particularly excellent water solubility, with a 4 wt% aqueous solution having a light transmittance at 660 nm of 92% or more.

[0127] <Animal testing (acetyl group residual rate, feed intake, weight gain, blood glucose level, cholesterol, triglycerides, epididymal fat)> Animal experiments were initiated using nine 7-week-old (150-170g body weight) Wistar male rats (Japan SLC Co., Ltd.) housed individually in stainless steel cages under conditions of a room temperature of 24±1°C, a relative humidity of 55±5°C, and a 12-hour light-dark cycle (lights on from 7:00 to 19:00).

[0128] After delivery, the rats were acclimated to a purified diet, AIN-93G (Reeves et al., Journal of Nutrition, 123, 1939-1951 (1993)), along with tap water for 3 days. Then, based on body weight (to ensure uniformity of the total weight of the rats in each group), they were divided into three groups: Group 1 (sometimes referred to as the "control group") received AIN-93G (also referred to as the "test group") containing 5 wt% low-substituted cellulose acetate (Example A-2); and Group 3 (sometimes referred to as the "comparison group") received AIN-93G (also referred to as the "low-substituted cellulose acetate" (Comparative Example A-1) containing 5 wt% low-substituted cellulose acetate (Comparative Example A-1) ad libitum with tap water for 14 days. Each group consisted of three rats. Group 1 corresponds to Reference Example B-1, Group 2 corresponds to Example B-1, and Group 3 corresponds to Comparative Example B-1.

[0129] The rats were divided into three groups, and on days 3, 7, and 13 after starting to feed each diet, all feces were collected for one day and analyzed for the residual acetyl group rate. The analytical method is as follows. In addition, feed intake and weight gain were measured throughout the feeding period.

[0130] On the 14th day of feeding, rats were fasted from 7:00 AM and autopsies were performed at 3:00 PM. Under isoflurane anesthesia, rats underwent laparotomy, and approximately 2 mL of blood was collected from the abdominal aorta into a heparinized test tube (Venoject II heparin sodium, 3 mL blood collection tube: Terumo Corporation). The rats were then exsanguinated and euthanized, and the epididymal fat (left and right) was promptly removed. The weight of the epididymal fat was then measured.

[0131] The collected blood was centrifuged at 2,380 G for 10 minutes at room temperature to separate the plasma. On the day of collection, the separated plasma was measured for blood glucose level using Shikaliquid GLU (Kanto Chemical Co., Ltd.), triglyceride level using Shikaliquid-N TG (Kanto Chemical Co., Ltd.), and cholesterol (also referred to as plasma cholesterol) using Shikaliquid-N CHO (Kanto Chemical Co., Ltd.).

[0132] <Acetyl group residual rate> 0.1 g of rat feces was suspended in 10 ml of water, and the acetic acid contained in the rat feces was derivatized to the corresponding 2-nitrophenylhydrazide using the method of Miwa et al. (Journal of Chromatography, 321, 165-174 (1985)). The 2-nitrophenylhydrazide of acetic acid was then quantified by HPLC analysis to determine the acetic acid concentration in the rat feces.

[0133] In addition, 0.1 g of rat feces was suspended in 150 mM aqueous sodium hydroxide solution and incubated at 70°C for 4 hours. The acetic acid contained in the sodium hydroxide-treated rat feces was derivatized to the corresponding 2-nitrophenylhydrazide using the method of Miwa et al. (Journal of Chromatography, 321, 165-174 (1985)), and the 2-nitrophenylhydrazide of acetic acid was quantified by HPLC analysis to determine the acetic acid concentration in the sodium hydroxide-treated rat feces.

[0134] The difference between the acetic acid concentration in the rat feces treated with sodium hydroxide and the acetic acid concentration in the rat feces was taken as the acetyl group concentration (moles per unit weight) of the rat feces. The residual acetyl group rate was calculated using the following formula: Residual acetyl group rate (mol%) = 100 × (acetyl group concentration in rat feces) × A / (B × C / D) A: Rat fecal volume (weight) from 0 to 24 hours B: Feed intake (weight) of rats from -24 hours to 0 hours C: Concentration of cellulose acetate in the feed (wt%) D: Number of moles of acetyl groups per unit weight of cellulose acetate =DS / (162.14+42.037×DS) DS: Total degree of acetyl substitution

[0135] [Table 2]

[0136] When rats were fed the cellulose acetate of Example A-2 (wherein the acetyl substitution degree at the 6-position was 18% or less of the total acetyl substitution degree) (Example B-1) on days 3, 7, and 13 of feeding, the residual acetyl group rate in the feces was lower than when rats were fed the cellulose acetate of Comparative Example A-1 (wherein the acetyl substitution degree at the 6-position was 36.9% or less of the total acetyl substitution degree) (Comparative Example B-1). This indicates that the cellulose acetate of the Example with a low acetyl substitution degree at the 6-position is highly degradable and easily metabolized in the body.

[0137] The feed intake of the rats in Comparative Example B-1 (comparison group) was significantly lower than that of Reference Example B-1 (control group), but no significant difference was observed in the amount of weight gain. On the other hand, the feed intake and weight gain of the rats in Example B-1 (test group) were both lower than those in Comparative Example B-1 (comparison group), and a clear significant difference was observed compared to Reference Example B-1 (control group).

[0138] The blood glucose level and cholesterol level of the rats in Example B-1 (test group) showed a tendency to decrease compared to those in Reference Example B-1 (control group), although the difference was not significant.

[0139] Furthermore, the triglycerides of the rats in Comparative Example B-1 (comparison group) were not significantly different from those in Reference Example B-1 (control group).On the other hand, the triglycerides of the rats in Example B-1 (test group) were lower than those in Reference Example B-1 (control group), and a significant difference was observed.

[0140] Furthermore, the epididymal fat of the rats in Comparative Example B-1 (comparison group) and Example B-1 (test group) was both lower than that of Reference Example B-1 (control group), and a significant difference was observed.

[0141] As described above, the cellulose acetate of the Examples, which has a low degree of acetyl substitution at the 6-position, is highly degradable and easily metabolized in the body, and is particularly effective in suppressing appetite (suppressing feed intake), weight gain, neutral fat, and fat accumulation (suppressing epididymal fat) in rats.

Claims

1. a total degree of acetyl substitution of 0.4 or more and 0.9 or less; Cellulose acetate having a ratio of the degree of acetyl substitution at the 6-position to the total degree of acetyl substitution of more than 0% and not more than 18%, a viscosity-average degree of polymerization of 3 or more and 400 or less, and a light transmittance of 660 nm of a 4 wt% aqueous solution of the cellulose acetate of 5% or more.

2. 2. The cellulose acetate according to claim 1, wherein the cellulose acetate has a light transmittance of 80% or more at 660 nm when measured in a 4% by weight aqueous solution.

3. 3. The cellulose acetate according to claim 1, which is obtained by solvolyzing raw cellulose acetate using sulfuric acid as an acid catalyst.

4. The cellulose acetate according to any one of claims 1 to 3, having a viscosity-average degree of polymerization of 15 or more and 150 or less.

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